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Title: Measuring droplet size of agriuclutral spray nozzles - Measurement distance and airspeed effects

Author
item Fritz, Bradley - Brad
item Hoffmann, Wesley
item BAGLEY, WILLIAM - Wilbur-Ellis Company
item KRUGER, GREG - University Of Nebraska
item CZACZYK, ZBIGNIEW - Poznan University Of Life Sciences
item HENRY, RYAN - University Of Nebraska

Submitted to: Atomization and Sprays
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2013
Publication Date: 7/28/2014
Citation: Fritz, B.K., Hoffmann, W.C., Bagley, W.E., Kruger, G., Czaczyk, Z., Henry, R. 2014. Measuring droplet size of agriuclutral spray nozzles - Measurement distance and airspeed effects. Atomization and Sprays. 24(9):747-760.

Interpretive Summary: With a number of new spray testing laboratories going into operation within the U.S. and each gearing up to measure spray atomization from agricultural spray nozzles using laser diffraction, establishing and following a set of scientific standard procedures is crucial to long term data generation and standardization across the industry. While offering ease of use as compared to other methods, laser diffraction measurements do not account for measurement bias effects due to differential velocities between differing sized spray droplets, and in many cases significantly overestimate the fine droplet portion of the spray. This work examined a number of measurement distances and horizontal airflow velocities to determine which methods introduce the least measurement bias and result in the most accurate droplet size data for both ground and aerial application droplet size studies. These methods provide for more accurate droplet size data for use in efficacy testing and drift assessments, and may allow for better inter-lab reproducibility.

Technical Abstract: With a number of new spray testing laboratories going into operation within the U.S. and each gearing up to measure spray atomization from agricultural spray nozzles using laser diffraction, establishing and following a set of scientific standard procedures is crucial to long term data generation and standardization across the industry. It has long been recognized, that while offering ease of use as compared to other methods, laser diffraction measurements do not account of measurement bias effects due to differential velocities between differing sized spray droplets, and in many cases significantly overestimate the fine droplet portion of the spray. Droplet sizes and velocities were measured for three agricultural flat fan nozzles (8002, 8008, and 6510) each a three spray pressures (138, 276 and 414 kPa) at four downstream distances (15.2, 30.5, 45.7 and 76.2 cm) across a range of concurrent air velocities (0.7 – 80.5 m/s). at air velocities below 6.7 m/s, large gradients in droplet velocities resulted in overestimation of both the 10% volume diameter (typically more than 10%) as well as percent volume of the spray less that 100 um or less (V <100) (typically two- to three-fold). A measurement distance of 30.5 cm with a concurrent air velocity of 6.7 m/s for ground nozzle testing and a measurement distance of 45.7 cm for aerial spray nozzle testing, reduced spatial bias in droplet size estimates (typically to 5% or less). Use of these methods provides for more accurate drop size data for use in efficacy testing and drift assessments, and it may allow for better inter-lab reproducibility.